1. Field of the Invention
The invention relates generally to the field of immunology and immunotherapy applications using oligoribonucleotides as immune modulatory agents. More particularly, the invention relates to immune modulatory RNA compositions and methods of use thereof for modulating the immune response through Toll-like receptor 8 (TLR8), Toll-like receptor 7 (TLR7) and TLR7 and TLR8.
2. Summary of the Related Art
The immune response involves both an innate and an adaptive response based upon the subset of cells involved in the response. For example, the T helper (Th) cells involved in classical cell-mediated functions such as delayed-type hypersensitivity and activation of cytotoxic T lymphocytes (CTLs) are Th1 cells, whereas the Th cells involved as helper cells for B-cell activation are Th2 cells. The type of immune response is influenced by the cytokines and chemokines produced in response to antigen exposure. Cytokines provide a means for controlling the immune response by affecting the balance of T helper 1 (Th1) and T helper 2 (Th2) cells, which directly affects the type of immune response that occurs. If the balance is toward higher numbers of Th1 cells, then a cell-mediated immune response occurs, which includes activation of cytotoxic T cells (CTLs). When the balance is toward higher numbers of Th2 cells, then a humoral or antibody immune response occurs. Each of these immune response results in a different set of cytokines being secreted from Th1 and Th2 cells. Differences in the cytokines secreted by Th1 and Th2 cells may be the result of the different biological functions of these two T cell subsets.
Th1 cells are involved in the body's innate response to antigens (e.g. viral infections, intracellular pathogens, and tumor cells). The initial response to an antigen can be the secretion of IL-12 from antigen presenting cells (e.g. activated macrophages and dendritic cells) and the concomitant activation of Th1 cells. The result of activating Th1 cells is a secretion of certain cytokines (e.g. IL-2, IFN-gamma and other cytokines) and a concomitant activation of antigen-specific CTLs. Th2 cells are known to be activated in response to bacteria, parasites, antigens, and allergens and may mediate the body's adaptive immune response (e.g. immunoglobulin production and eosinophil activation) through the secretion of certain cytokines (e.g. IL-3, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13 and other cytokines) and chemokines. Secretion of certain of these cytokines may result in B-cell proliferation and an increase in antibody production. In addition, certain of these cytokines may stimulate or inhibit the release of other cytokines (e.g IL-10 inhibits IFN-γ secretion from Th1 cells and IL-12 from dendritic cells). Ultimately, the balance between Th1 and Th2 cells and the cytokines and chemokines released in response to selected stimulus can have an important role in how the body's immune system responds to disease. For example, IFN-α may inhibit hepatitis C, and MIP-1α and MIP-1 (also known as CCL3 and CCL4 respectively) may inhibit HIV-1 infection. Optimal balancing of the Th1/Th2 immune response presents the opportunity to use the immune system to treat and prevent a variety of diseases.
The Th1 immune response can be induced in mammals for example by introduction of bacterial or synthetic DNA containing unmethylated CpG dinucleotides, which immune response results from presentation of specific oligonucleotide sequences (e.g. unmethylated CpG) to receptors on certain immune cells known as pattern recognition receptors (PRRs). Certain of these PRRs are Toll-like receptors (TLRs).
TLRs are intimately involved in inducing the innate immune response in response to microbial infection. In vertebrates, TLRs consist of a family of ten proteins (TLR1 to TLR10) that are known to recognize pathogen associated molecular patterns. Of the ten, TLR3, 7, 8, and 9 are known to localize in endosomes inside the cell and recognize nucleic acids (DNA and RNA) and small molecules such as nucleosides and nucleic acid metabolites. TLR3 and TLR9 are known to recognize nucleic acid such as dsRNA and unmethylated CpG dinucleotide present in viral and bacterial and synthetic DNA, respectively. Bacterial DNA has been shown to activate the immune system and to generate antitumor activity (Tokunaga T et al., J. Natl. Cancer Inst. (1984) 72:955-962; Shimada S, et al., Jpn. H cancer Res, 1986, 77, 808-816; Yamamoto S, et al., Jpn. J. Cancer Res., 1986, 79, 866-73; Messina, J, et al., J. Immunolo. (1991) 147:1759-1764). Other studies using antisense oligonucleotides containing CpG dinucleotides have shown stimulation of an immune response (Zhao Q, et al., Biochem. Pharmacol. 1996, 26, 173-82). Subsequent studies showed that TLR9 recognizes unmethylated CpG motifs present in bacterial and synthetic DNA (Hemmi H, et al., Nature. (2000) 408:740-5). Other modifications of CpG-containing phosphorothioate oligonucleotides can also affect their ability to act through TLR9 and modulate the immune response (see, e.g., Zhao et al., Biochem. Pharmacol. (1996) 51:173-182; Zhao et al., Biochem Pharmacol. (1996) 52:1537-1544; Zhao et al., Antisense Nucleic Acid Drug Dev. (1997) 7:495-502; Zhao et al., Bioorg. Med. Chem. Lett. (1999) 9:3453-3458; Zhao et al., Bioorg. Med. Chem. Lett. (2000) 10:1051-1054; Yu et al., Bioorg. Med. Chem. Lett. (2000) 10:2585-2588; Yu et al., Bioorg. Med. Chem. Lett. (2001) 11:2263-2267; and Kandimalla et al., Bioorg. Med. Chem. (2001) 9:807-813). In addition, structure activity relationship studies have allowed identification of synthetic motifs and novel DNA-based structures that induce specific immune response profiles that are distinct from those resulting from unmethylated CpG dinucleotides. (Kandimalla E R, et al., Proc Natl Acad Sci USA. (2005) 102:6925-30. Kandimalla E R, et al., Proc Natl Acad Sci USA. (2003) 100:14303-8. Cong Y P, et al., Biochem Biophys Res Commun. (2003) 310:1133-9. Kandimalla E R, et al., Biochem Biophys Res Commun. (2003) 306:948-53. Kandimalla E R, et al., Nucleic Acids Res. (2003) 31:2393-400. Yu D, et al., Bioorg Med Chem. (2003) 11:459-64. Bhagat L, et al., Biochem Biophys Res Commun. (2003) 300:853-61. Yu D, et al., Nucleic Acids Res. (2002) 30:4460-9. Yu D, et al., J Med Chem. (2002) 45:4540-8. Yu D, et al., Biochem Biophys Res Commun. (2002) 297:83-90. Kandimalla E R, et al., Bioconjug Chem. (2002) 13:966-74. Yu D, K et al., Nucleic Acids Res. (2002) 30:1613-9. Yu D, et al., Bioorg Med. Chem. (2001) 9:2803-8. Yu D, et al., Bioorg Med Chem Lett. (2001) 11:2263-7. Kandimalla E R, et al., Bioorg Med Chem. (2001) 9:807-13. Yu D, et al., Bioorg Med Chem Lett. (2000) 10:2585-8, Putta M R, et al., Nucleic Acids Res. (2006) 34:3231-8). However, until recently, natural ligands for TLR7 and TLR8 were unknown.
It has been shown that TLRs 7 and 8 recognize viral and synthetic single-stranded RNAs and small molecules, including a number of nucleosides (Diebold, S. S., et al., Science v: 303, 1529-1531 (2004). Diebold et al. (Science, 303:1529-1531 (2004)) show that the IFN-α response to influenza virus requires endosomal recognition of influenza genomic RNA and signaling by means of TLR7 and MyD88 and identify ssRNA as a ligand for TLR7. Certain synthetic compounds, the imidazoquinolones, imiquimod (R-837) and resiquimod (R-848) are ligands of TLR7 and TLR8 (Hemmi H et al., (2002) Nat Immunol 3:196-200; Jurk M et al., (2002) Nat Immunol 3:499). In addition, certain guanosine analogs, such as 7-deaza-G, 7-thia-8-oxo-G (TOG), and 7-allyl-8-oxo-G (loxoribine), have been shown to activate TLR7 at high concentrations (Lee J et al., Proc Natl Acad Sci USA. 2003, 100:6646-51). However, these small molecules, eg. imiquimod, are also known to act through other receptors (Schon M P, et al., (2006) J. Invest Dermatol., 126, 1338-47)
The lack of any known specific ssRNA motif for TLR7 or TLR8 recognition and the potentially wide range of stimulatory ssRNA molecules suggest that TLR7 and TLR8 can recognize both self and viral RNA. Recently it was shown that certain GU-rich oligoribonucleotides are immunostimulatory and act through TLR7 and TLR8 (Heil et al. Science, 303: 1526-1529 (2004); Lipford et al. WO03/086280; Wagner et al. WO98/32462) when complexed with N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N trimethylammoniummethylsulfate (DOTAP) or other lipid agents. However, RNA molecules have been used for many years, for example as ribozymes and, more recently, siRNA and microRNA, and RNA employed as ribozymes, siRNA, and microRNA contain GU dinucleotides. In addition, a number these RNA molecules have been shown to elicit immune responses through TLR stimulation in the presence of lipids (Kariko et al., Immunity (2005) 23:165-75; Ma Z et al., Biochem Biophys Res Commun., (2005) 330, 755-9). However, the instability of these RNA molecules has hindered progress in using and applying these molecules in many areas (e.g. prevention and treatment of human disease).
Oligonucleotides and oligodeoxynucleotides containing a ribose or deoxyribose sugar have been used in a wide variety of fields, including but not limited to diagnostic probing, PCR priming, antisense inhibition of gene expression, siRNA, microRNA, aptamers, ribozymes, and immunotherapeutic agents based on Toll-like Receptors (TLRs). More recently, many publications have demonstrated the use of oligodeoxynucleotides as immune modulatory agents and their use alone or as adjuvants in immunotherapy applications for many diseases, such as allergy, asthma, autoimmunity, cancer and infectious disease.
The fact that DNA oligonucleotides are recognized by TLR9, while RNA oligonucleotides are recognized by TLR7 and/or TLR8 is most likely due to differences in the structural conformations between DNA and RNA. However, the chemical differences between DNA and RNA also make DNA far more chemically and enzymatically stable than RNA.
RNA is rapidly degraded by ubiquitous extracellular ribonucleases (RNases) which ensure that little, if any, self-ssRNA reaches the antigen-presenting cells. Exonuclease degradation of nucleic acids is predominantly of 3′-nuclease digestion with a smaller percentage through 5′-exonuclease action. In addition to exonuclease digestion, RNA can also be degraded by endonuclease activity of RNAses. RNA-based molecules have so far had to be complexed with lipids to provide stability against nucleases.
While providing an essential function of preventing autoimmune reactivity, these ribonucleases also present a substantial problem for any synthetic ssRNA molecule designed to be exploited for immunotherapy, as ribonucleases will rapidly degrade both synthetic and natural ssRNA. To overcome this hurdle, protection of ssRNA molecules from degradation has been attempted by encapsulating the ssRNA in lipsomes, condensing it with polyethylenimine, or complexing it to molecules such as N-[1-(2,3 dioleoyloxy)-propyl]-N,N,N-trimethylammonium methyl-sulfate (DOTAP). However, these protective measures are secondary measures applied to a still unstable ssRNA, and the effects of these protective measures on the in vivo efficacy and immune modulatory activity of ssRNA (natural or synthetic) remain unclear.
Agrawal et al. (Ser. No. 11/697,422) describe a novel class of SIMRA compositions. However, a challenge remains to develop additional compounds that retain the naked RNA such that it continues to be recognized as a ligand for TLR7 and/or TLR8, while improving its stability such that it can be made to be a useful in vivo molecule. Ideally, this challenge might be met through the design of inherently stable RNA-based molecules that can act as new immunotherapic agents, which will find use in a number of clinically relevant applications, such as improving the effects of vaccination when co-administered or treating and/or preventing diseases when invoking or enhancing an immune response is beneficial, for example cancer, autoimmune disorders, airway inflammation, inflammatory disorders, infectious diseases, skin disorders, allergy, asthma or diseases caused by pathogens.